General

Liner Description

The thermoplastic liner system described in this report combines layers of materials that allow the total structure to behave homogeneously, but with a combination of the properties provided by the individual materials. The liner relies on the host pipe to provide mechanical strength, while the liner provides corrosion protection. In plasticlined steel, for example, the corrosion/erosion resistance of the inner plastic pipe and the strength/mechanical durability of the metal case are both exploited. This allows for design pressures equal to those of the host pipe.

Plastic-lined steel is differentiated from plastic-coated steel in that:

1. The thickness of plastic coatings is measured in mils (thousandths of an inch), whereas liners typically vary from 0.125 to 1.00 in. (3.2 to 25 mm) in thickness.

2. The critical manufacturing variable in coated systems is the adhesion to the substrate metal, whereas for liners, attaining a mechanically fitted cohesive unit is the critical element.

3. A plastic coating retains little, if any, mechanical strength, whereas the liner itself has pressurecontaining structural integrity.

Installation Methods

The installation of a liner into a host pipe involves mechanically fitting two piping systems together so they will act as a single unit.

The systems currently being used in the oilfield for pipelines can be generally described as follows:

1. The liner is hydraulically and thermally expanded radially out to the steel pipe following insertion.

2. The liner is installed after a temporary diameterreduction process. After completion of the insertion, the liner expands to the internal diameter of the steel pipe.